title: Functional sensitivity of polar surfaces on transmembrane helix 8 and cytoplasmic loop 8-9 of the Escherichia coli GABA (4-aminobutyrate) transporter encoded by gabP: mutagenic analysis of a consensus amphipathic region found in transporters from bacteria to mammals.
abstract: The gab permease (GabP) catalyses transport of GABA (4-aminobutyrate) into Escherichia coli. Although GabP can recognize and transport many GABA analogues that exhibit activity at GABAergic synapses in the nervous system, the protein domains responsible for these transport and ligand recognition properties have not been studied. Here we report that an amphipathic domain extending through putative transmembrane helix 8 and into the adjoining cytoplasmic region (loop 8-9) contains a critical 20 residue zone within which mutagenesis of polar amino acids has a deleterious effect on [3H]GABA transport activity. This functionally important amphipathic domain is found to be highly conserved in the many APC family transporters that are homologous to GabP. And even though members of the GAT family of GABA transporters from the animal nervous system are not homologous to GabP, an analogous amphipathic structure is found in their loop 8-9 region. These results and observations suggest: (1) that the consensus amphipathic region (CAR) in the putative helix 8 and loop 8-9 region of GabP has functional significance, and (2) that nature has repeatedly used this CAR in transporters from bacteria to mammals.
authors.affiliation: Department of Physiology and Biophysics, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0641, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Hu
authors.forename: S C
authors.initials: SC
authors.lastname: King
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D016384:Consensus Sequence; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D019143:Evolution, Molecular; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D027361:Organic Anion Transporters; D013499:Surface Properties
chemical_list: D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C513601:gabP protein, E coli